Ultrafast vortex rotating light field generator

Abstract

The present invention is applicable to the field of ultrafast optics and light field control technology, and provides an ultrafast vortex rotating light field generating device, comprising: a light source system for generating linearly polarized femtosecond laser pulses; a vortex chirped laser pulse generating system for generating vortex chirped laser pulses based on the femtosecond laser pulses; a pulse pair generating and interfering system for generating pulse pairs with different frequencies and opposite topological charges based on the vortex chirped laser pulses, and combining and interfering the pulse pairs to generate an ultrafast vortex rotating light field. The present invention utilizes vortex chirped laser pulse pair interference to generate an ultrafast vortex rotating light field, and the rotation speed is determined by the beat frequency δω of the vortex chirped laser pulse pair, which can reach 10 13 rad / s level, and the corresponding rotation frequency reaches the terahertz level and can be tuned.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrafast optics and light field control, and in particular relates to an ultrafast vortex rotating light field generating device. Background Art

[0002] Ultrafast vortex rotating light fields are special light fields whose spatial structures rotate at high speeds over time and are determined by their orbital angular momentum. Most techniques for generating such light fields use the interference of two vortex beams, and their angular velocity can be adjusted by controlling the relative phase difference between the two vortex beams.

[0003] If the rotating light field has super-strong light intensity and terahertz (terahertz, 10 12 The rotation rate is on the order of Hz, which can be applied in many fields such as laser precision processing, plasma accelerators, strong terahertz radiation, and simulation of the evolution process of celestial phenomena in the laboratory.

[0004] For example, laser percussion drilling is currently commonly used in laser micro-hole processing. Hard and brittle materials such as ceramics and glass are prone to cracking, wrinkling, and other structures due to internal tension, thermal shock, and other factors. This leads to uneven processing, reduces the roundness and consistency of the micro-holes, and affects the quality of the micro-holes. A laser processing head with a rotating beam, similar to a rotating optical drill, can effectively eliminate such processing defects, thereby improving the smoothness and uniformity of the sidewalls of laser drilling and laser cutting. Therefore, the development of a device for generating ultrafast vortex rotating light fields will be of great use in many fields such as laser precision processing.

[0005] Existing technologies use spatial light modulators to introduce a frequency difference between two vortex beams, achieving rotating fields with frequencies ranging from tens of hertz to hundreds of megahertz. While electro-optic modulators and axially symmetric polarization elements can achieve much faster optical field rotation speeds than spatial light modulators, they are still limited to the gigahertz range due to the bandwidth limitations of electro-optical modules. Consequently, ultrafast vortex rotating optical fields with rotation speeds reaching the terahertz range have yet to be developed. Summary of the Invention

[0006] The technical problem to be solved by the present invention is how to provide an ultrafast vortex rotating light field device with a rotation rate reaching the terahertz level and being tunable.

[0007] To solve the above technical problems, the embodiment of the present invention is implemented as follows: an ultrafast vortex rotating light field generating device, comprising:

[0008] a light source system for generating linearly polarized femtosecond laser pulses;

[0009] A vortex chirped laser pulse generation system, configured to generate vortex chirped laser pulses based on the femtosecond laser pulses;

[0010] The pulse pair generation and interference system is used to generate pulse pairs with different frequencies and opposite topological charges based on the vortex chirped laser pulses, and to combine and interfere the pulse pairs to generate an ultrafast vortex rotating light field.

[0011] As can be seen from the above examples, the present invention utilizes the interference of vortex-chirped laser pulse pairs to generate an ultrafast vortex rotating light field. The rotation speed is determined by the beat frequency δω of the vortex-chirped laser pulse pairs and can reach the order of 1013 rad / s. The corresponding rotation frequency reaches the terahertz level and is tunable. Therefore, the present invention can achieve an ultrafast rotating light field with a rotation rate that is tunable at the terahertz level. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 1 is a schematic diagram of the structure of an ultrafast vortex rotating light field generating device provided by the first embodiment of the present invention;

[0013] Figure 2 is a structural diagram of a vortex phase generator provided by a first embodiment of the present invention;

[0014] Figure 3 2 is a schematic diagram showing the structure of an ultrafast vortex rotating light field generating device provided by a second embodiment of the present invention; DETAILED DESCRIPTION

[0015] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0016] Reference Figure 1 The ultrafast vortex rotating light field generating device provided by the first embodiment of the present invention includes a light source system 11, a vortex chirped laser pulse generating system 12, and a pulse pair generating and interfering system 13 in sequence along the light path direction.

[0017] Among them, the light source system 11 is used to generate and output linearly polarized femtosecond laser pulses. As an example, a titanium sapphire femtosecond laser can be specifically selected. The central wavelength of the femtosecond laser pulse output by the titanium sapphire femtosecond laser is around 800nm, the pulse width is on the order of tens of femtoseconds, and the corresponding spectral width is on the order of tens of nanometers.

[0018] The vortex-chirped laser pulse generation system 12 is used to generate vortex-chirped laser pulses based on the femtosecond laser pulses output by the light source system 11. A chirped laser pulse refers to a laser pulse whose instantaneous frequency varies with time, and the word "vortex" refers to the light field pattern of the chirped laser pulse as a vortex light carrying orbital angular momentum. The overall wavefront exhibits a spiral shape, rotating around an axis in space during propagation. The specific principle is that the vortex-chirped laser pulse generation system 12 first stretches the femtosecond laser pulse output by the light source system 1, and then modulates the stretched laser pulse into a vortex-chirped laser pulse.

[0019] Reference Figure 1 As an implementation method, the vortex chirped laser pulse generating system 12 may further include a pulse stretcher 121 and a vortex phase generator 122. The pulse stretcher 121 is used to stretch the femtosecond laser pulse output by the light source system 11 into a picosecond chirped laser pulse, and the vortex phase generator 122 is used to modulate the picosecond chirped laser pulse into a vortex chirped laser pulse.

[0020] Pulse stretcher 121 can be a commonly used pulse disperser, which stretches the femtosecond laser pulse by utilizing its dispersion characteristics. For example, the aforementioned tens-of-femtosecond laser pulse can be stretched into a chirped picosecond laser pulse. Of course, in practice, femtosecond laser pulses can be stretched to any desired pulse width based on actual needs.

[0021] In this embodiment, the structure of the vortex phase generator 122 is as follows: Figure 2 As shown, it includes a first quarter-wave plate 1221, a half-wave plate 1222 (also called a Q-plate), and a second quarter-wave plate 1223, which are sequentially arranged along the optical path. The first quarter-wave plate 1221 is used to convert the polarization state of the picosecond chirped laser pulse obtained by pulse stretcher 121 from linear polarization to circular polarization; the half-wave plate 1222 is used to form a vortex beam from the picosecond chirped laser pulse converted into circular polarization, wherein the direction of the fast axis of the half-wave plate 1222 is related to its azimuth angle; the second quarter-wave plate 1223 is used to modulate the vortex beam into a linearly polarized vortex chirped laser pulse, the topological charge of which is represented by l.

[0022] The pulse pair generation and interference system 13 is used to generate pulse pairs with different frequencies and opposite topological charges based on the vortex chirped laser pulses, and to combine the pulse pairs for interference to produce an ultrafast vortex rotating light field. The principle is to first split the vortex chirped laser pulse into two pulses, then process the two pulses into two beams with opposite topological charges. The frequency of one of the beams is then changed to obtain two beams with opposite topological charges and different frequencies, which serve as the pulse pair for subsequent beam combining and interference.

[0023] Based on the first embodiment, Figure 3 The structure of the ultrafast vortex rotating light field generating device provided by the second embodiment of the present invention is further shown. Figure 2 The medium vortex chirped laser pulse generation system also includes a first reflector assembly consisting of a reflector 1231 and a reflector 1232. The first reflector assembly is arranged between the pulse stretcher 121 and the vortex phase generator 122, and is used to reflect the picosecond chirped laser pulse to the vortex phase generator 122.

[0024] The first reflector assembly can be a single reflector or a combination of multiple reflectors. Its primary function is to change the direction of light beam propagation, thereby reducing the overall length or thickness of the device, facilitating product design and installation. Similarly, refractive optical devices can also be used to change the direction of light beam propagation, achieving the same effect. Of course, if product size is not a concern, the first reflector assembly can be omitted.

[0025] in addition, Figure 2 The linearly polarized vortex chirped laser pulse output from the vortex phase generator 122 is directly input into the pulse pair generation and interference system 13. Of course, in specific implementation, a reflection device and a refraction device can be added between the vortex phase generator 122 and the pulse pair generation and interference system 13 according to the relative position relationship between the two to change the optical path so as to meet the corresponding needs.

[0026] In this embodiment, the pulse pair generation and interference system 13 includes: a first bandpass filter 131, a transmitted light beam reflection component 132, an optical delay device 133, a reflected light beam reflection component 134, a second bandpass filter 135 and a non-polarization beam splitter-combiner 136.

[0027] The first band-pass filter 131 is used to split the vortex chirped laser pulse into a transmitted light beam pulse and a reflected light beam pulse.

[0028] The transmitted beam reflection assembly 132 is used to reflect the transmitted beam pulses a first number of times. It may include at least one reflector, each mirror sequentially positioned along the optical path between the light-exiting side of the transmitted beam pulses of the first bandpass filter 132 and the optical retarder 133, to reflect the transmitted beam toward the optical retarder. The "first number" can be any number, meaning that the transmitted beam pulses can be reflected any number of times, but the second number of reflections of the subsequent reflected beam pulses must satisfy the condition of being an even number.

[0029] The optical delay device 133 is used to delay the transmitted light beam pulse after the first number of reflection processes so as to synchronize it with the reflected light beam pulse, thereby obtaining a first light beam pulse used for interference. Figure 3 The optical retarder 133 is composed of two highly reflective mirrors and can be placed on a precision displacement platform.

[0030] The reflected beam reflecting assembly 134 may include at least one reflector, each mirror sequentially positioned along the optical path between the light-exiting side of the transmitted beam pulse of the first bandpass filter 132 and the light-entering side of the second bandpass filter 135, to process the reflected beam pulse through a second number of reflections. Similar to the "first number" described above, the "second number" here can also be any number, meaning that the reflected beam pulse can be reflected any number of times. However, the "first number" and "second number" must be odd or even to ensure that the topological charge of the reflected beam is opposite to that of the transmitted beam pulse.

[0031] For example, the number of reflectors in the transmitted light beam reflecting assembly 132 is an odd number, while the number of reflectors in the reflected light beam reflecting assembly 134 is an even number, or the number of reflectors in the transmitted light beam reflecting assembly 132 is an even number, while the number of reflectors in the reflected light beam reflecting assembly 134 is an odd number. Figure 3 In the figure, only the example in which the transmitted light beam reflecting component 132 includes one reflecting mirror and the reflected light beam reflecting component 134 includes two reflecting mirrors is shown.

[0032] The second bandpass filter 135 has a central pass frequency different from that of the first bandpass filter and is used to filter the reflected light beam pulses after the second number of reflections to obtain second light beam pulses for interference. The first and second light beam pulses form a synchronized pulse pair with a preset frequency difference and opposite topological charges.

[0033] The first and second bandpass filters 131 and 135 are designed to have different central pass frequencies to achieve different frequencies for the aforementioned pulse pairs. For example, the first bandpass filter 131 transmits a central wavelength of 805 nm and a bandwidth of 10 nm. After beam splitting by the first bandpass filter 131 and undergoing an odd and even number of reflections, the topological charges l1 and l2 of the reflected and transmitted beams are opposite. The second bandpass filter 135 transmits a central wavelength of 795 nm and a bandwidth of 10 nm.

[0034] The non-polarization beam splitter-combiner 136 has a splitting ratio of 50:50 and is used to receive the first light beam pulse and the second light beam pulse through its two orthogonal directions, so that the first light beam pulse and the second light beam pulse are combined and interfered in their two orthogonal directions to form an ultrafast vortex rotating light field.

[0035] The transmitted light beam and the reflected light beam incident on the non-polarization beam splitter-combiner 136 are a pair of vortex chirped pulse pairs with a certain frequency difference, opposite topological charge and synchronization. This pulse pair can interfere in the two orthogonal directions of the non-polarization beam splitter-combiner 136 to form an ultrafast vortex rotating light field.

[0036] The specific interference light field distribution is described as E(r,θ,t), where r represents the radial coordinate, θ represents the azimuth angle, and t represents time. The formula is as follows:

[0037] E(r,θ,t)=E1exp[i(ω1-Δω)t]·exp(il1θ)+E2exp[i(ω1-Δω)t]·exp(il2θ).

[0038] Where exp represents an exponential function with the natural constant e as the base, subscripts 1 and 2 represent the transmitted light beam and the reflected light beam after passing through the first bandpass filter 131, respectively, E, ω, and l represent the complex amplitude, center frequency, and topological charge, respectively, Δω represents the center frequency offset of the interference, and i represents the imaginary unit.

[0039] The angular velocity of the ultrafast rotating light field is obtained as Ω, Ω = dθ / dt = δω / |l1-l2|.

[0040] The beat frequency between the two interfering pulse pairs is δω=|ω1-ω2±2Δω|.

[0041] By adjusting the precision displacement platform on which the optical delay device 133 is placed, when the vortex chirped pulse pair is precisely synchronized, the frequency difference δω=ω1-ω2≈3×10 13 rad / s, assuming that l1 and l2 are ±1 respectively, an ultrafast rotating light field with a rotation rate Ω reaching 1.5 THz is obtained. By adjusting the precision displacement platform and the topological charge, the beat frequency difference δω of the vortex picosecond chirped pulse pair can be adjusted within 10 12 rad / s~10 13 The rad / s range is adjustable, and the resulting ultrafast rotating light field rate is adjustable between 0.1 and 3 THz. The spatial spot pattern of the ultrafast rotating light field is determined by the topological charge of the pulse pair. By adjusting the optical retarder 133 to control the center frequency offset of the interference between the two vortex chirped pulses and setting the center wavelength of the first and second bandpass filters 131 and 135, that is, controlling the beat frequency δω of the pulse pair, an ultrafast rotating light field with a rotation rate tunable to the terahertz level can be achieved.

[0042] In summary, the present invention utilizes the interference of vortex chirped pulse pairs formed by two bandpass filters to generate an ultrafast rotating light field. The rotation speed is determined by the beat frequency δω of the vortex chirped pulse pair and can reach 10 13rad / s level, and the corresponding rotation frequency reaches the terahertz level, which can be tuned by an optical delay device. Therefore, the present invention can realize an ultrafast rotating light field with a rotation rate reaching the THz level and being tunable.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An ultrafast vortex rotating light field generating device, characterized in that: include: a light source system for generating linearly polarized femtosecond laser pulses; A vortex chirped laser pulse generation system, configured to generate vortex chirped laser pulses based on the femtosecond laser pulses; A pulse pair generation and interference system for generating pulse pairs with different frequencies and opposite topological charges based on the vortex chirped laser pulses, and combining and interfering the pulse pairs to generate an ultrafast vortex rotating light field; comprising a first bandpass filter, a transmitted beam reflection component, an optical delay, a reflected beam reflection component, a second bandpass filter, and a non-polarization beam splitter-combiner, wherein: a first bandpass filter, configured to split the vortex chirped laser pulse into a transmitted beam pulse and a reflected beam pulse; a transmitted light beam reflection component, configured to process the transmitted light beam pulses through a first number of reflections; an optical delay device placed on an adjustable precision displacement platform, configured to delay the transmitted light beam pulse after the first number of reflections so as to be synchronized with the reflected light beam pulse by adjusting the precision displacement platform, thereby obtaining a first light beam pulse used for interference; a reflected light beam reflecting component, configured to reflect the reflected light beam pulse a second number of times; wherein the first number of times and the second number of times are odd and even, so that the topological charge of the reflected light beam is opposite to the topological charge of the transmitted light beam pulse; a second bandpass filter having a central pass frequency different from that of the first bandpass filter, and configured to filter the reflected light beam pulses after the second number of reflections to obtain second light beam pulses for interference; the first light beam pulses and the second light beam pulses forming a pulse pair having a preset frequency difference, opposite topological charges, and being synchronized; A non-polarization beam splitter-combiner, having a splitting ratio of 50:50, is used to receive the first light beam pulse and the second light beam pulse through its two orthogonal directions, so that the first light beam pulse and the second light beam pulse are combined and interfered in their two orthogonal directions to form an ultrafast vortex rotating light field.

2. The ultrafast vortex rotating light field generating device according to claim 1, characterized in that: The vortex chirped laser pulse generation system comprises: A pulse stretcher, used for stretching the femtosecond laser pulse into a picosecond chirped laser pulse; A vortex phase generator is used to modulate the picosecond chirped laser pulse into a vortex chirped laser pulse.

3. The ultrafast vortex rotating light field generating device according to claim 2, characterized in that: The vortex chirped laser pulse generation system further includes: a first reflector assembly; The first reflector assembly is arranged between the pulse stretcher and the vortex phase generator, and is used for reflecting the picosecond chirped laser pulse to the vortex phase generator.

4. The ultrafast vortex rotating light field generating device according to claim 2, characterized in that: The pulse stretcher is a pulse disperser.

5. The ultrafast vortex rotating light field generating device according to claim 2, characterized in that: The vortex phase generator includes a first quarter wave plate, a half wave plate, and a second quarter wave plate arranged in sequence along the optical path direction; The first quarter-wave plate is used to convert the polarization state of the picosecond chirped laser pulse from linear polarization to circular polarization; The half-wave plate is used to form a vortex beam from the picosecond chirped laser pulse converted into circular polarization; The second quarter-wave plate is used to modulate the vortex light beam into a linearly polarized vortex chirped laser pulse.

6. The ultrafast vortex rotating light field generating device according to claim 1, characterized in that: The transmitted light beam reflecting assembly includes an odd number of reflecting mirrors, and the reflected light beam reflecting assembly includes an even number of reflecting mirrors.

7. The ultrafast vortex rotating light field generating device according to claim 1, characterized in that: The transmitted light beam reflecting assembly includes an even number of reflecting mirrors, and the reflected light beam reflecting assembly includes an odd number of reflecting mirrors.

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